PTL 1 discloses a technique in which an image of a product carried on a belt conveyor within a casing for blocking external light is captured by a color image capture camera at a predetermined time interval while the product is being illuminated by an illumination device and white balance is adjusted based on the captured image. Adjusting white balance refers to a function of color correction to make a white object look white and corrects a color difference in a white material caused by different light sources (e.g., sunlight and an electric lamp).